The proposed work for the coming year will deal with further investigation of the normal, functional state of the canine gastric epithelium in an attempt to understand the events occurring within the same epithelium under erosive or ulcerogenic conditions. Mucus secretion will be quantitated stereologically and biochemically. X-ray microdispersive and histochemical analysis will be used to examine the existence of heterogeneous populations of granules within the same cell by localizing sulfated glycoproteins. An attempt will be made to correlate changes in 3H thymidine incorporation with mucus secretion in order to investigate feedback mechanisms operating between surface mucus cells and progenitor cells. Lastly, calcium concentration, localization, and movement will be determined in mucus cells using x-ray probe microanalysis in order to examine intracellular ion movement during secretion.